Expression of laminin and its receptor LBP-32 in human and rat hepatoma cells.

Dramatic cellular changes that occur during hepatocarcinogenesis are associated with major alterations in extracellular matrix formation and in the relationships between cells and their microenvironment. We have studied the expression of laminin, the major noncollagenous glycoprotein of basement membrane, and the laminin receptor 32 kD laminin-binding protein in two rat (Faza 967 and HTC) and two human (HepG2 and HBGC2) hepatoma cell lines that express a variety of liver-specific functions. Laminin was found in the rough endoplasmic reticulum of these cells when the indirect immunoperoxidase method and electron microscopic examination were used. Radiolabeled laminin, immunoprecipitated from both media and cell extracts, was resolved by electrophoresis on sodium dodecyl sulfate gel in two major polypeptides that comigrated with the A and B subunits from Engelbreth-Holm-Swarm tumor laminin. Immunoblot analysis showed that the Mr = 400,000 polypeptide did not correspond to the A subunit of laminin. Northern blot analyses demonstrated large amounts of B1 and B2 mRNAs but no A chain mRNA. We conclude that the tumor cells produce the laminin B chains only. In contrast, normal adult hepatocytes from either man or rat lacked laminin mRNAs, whereas in 1-day primary culture, B chain mRNAs became detectable. The steady-state level of 32 kD laminin-binding protein mRNA was 10-fold and threefold higher in rat hepatoma cells than in freshly isolated and 1-day cultured normal rat hepatocytes, respectively. In human hepatocytes, the steady-state levels of 32 kD laminin-binding protein mRNAs varied depending on the donor and never reached the level of the human hepatoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)